1. Field of the Invention
The present invention relates to a high-voltage AC power supply having means for limiting peak capacitive current to a load having a substantial capacitive component, and more particularly, to such an AC power supply including a pulse-width modulated inverter and means for synthesizing a trapezoidal inverter output voltage waveform to be supplied to a complex load, such as, for example, a corotron in a reprographic machine.
2. Description of the Prior Art
High-frequency inverter circuits are often used to convert DC electrical energy to AC electrical energy. In many applications, a square wave output is desirable either for functional considerations or because of the simplicity of not requiring costly filters, and the like, necessary to produce a sine wave output.
A square wave output may be generated from various types of inverter circuits such as half-bridge, full-bridge, flyback, and the like. In all cases, the rise and fall times of the square waveform are controlled by the switching times of various types of semiconductor devices and by passive LCR circuit components necessary to a given design. Because of this, the rise and fall times generally assume an exponential form which, in turn, produces high peak currents in a load having a substantial capacitive component, as for example, in a complex load such as a charge corotron useful in reprographic machines. An exponential waveform, in turn, can produce severe stresses on semiconductors required to handle the current.
It is desirable, in high-voltage AC power supplies having inverter circuits for converting DC electrical energy to AC electrical energy, to maintain peak capacitive currents as small as possible in an effort to reduce the stress on the switching transistors thereby to improve the overall reliability of the power supply. Most present day inverter circuits accomplish this by slowing down the rise and fall times of the inverter circuit; this can have other adverse affects such as increasing losses in the inverter circuit.
It is, therefore, an object of the present invention to accomplish the lowering of the aforementioned peak capacitive currents from a high-voltage AC power supply to a load having a substantial capacitive component without sacrificing rise times and circuit efficiency, thereby to improve circuit reliability.